ADC Vref

[srob]

Wish to measure three small voltages (<1V) on a 16f676. Set Vref to 1.023V, but found the reading fluctutes with an injected voltage of 100mV on AN1. Checked AN1 ok with internal vref. This raises two questions:

1. What is the lowest practical value of Vref for the ADC to work correctly?

2. Does Vref require a buffer or filter capacitor - Checked with scope and Vref looked smooth?

Thanks

[mister_e]

Any code and schematic are welcome ;)

[JD123]

Microchip's web site ahs an excellent 20 minute video on designing AD circuits. I can't place a direct link due to their .aspx, but search their site for "Techniques that Reduce System Noise in ADC Circuits"

[rhino]

Microchip's web site ahs an excellent 20 minute video on designing AD circuits. I can't place a direct link due to their .aspx, but search their site for "Techniques that Reduce System Noise in ADC Circuits"

Go to http://techtrain.microchip.com/webseminars/QuickList.aspx and search for "Techniques That Reduce System Noise in ADC Circuits". You'll find the information JDM123 is referring to.